1. Field of the Invention
This invention relates to dynamically vulcanized blends having improved heat aging characteristics. Such blends can be used as toughened plastics or thermoplastic elastomers. A thermoplastic elastomer is generally defined as a polymer or blend of polymers that can be processed and recycled in the same way as a conventional thermoplastic material, yet has properties and performance similar to that of vulcanized rubber at service temperatures. Blends or alloys of plastic and elastomeric rubber have become increasingly important in the production of high performance thermoplastic elastomers, particularly for the replacement of thermoset rubber in various applications.
2. Description of the Related Art
Polymer blends which have a combination of both thermoplastic and elastic properties are generally obtained by combining a thermoplastic resin with an elastomeric composition in a way such that the elastomer is intimately and uniformly dispersed as a discrete particulate phase within a continuous phase of the thermoplastic. Early work with vulcanized compositions is found in U.S. Pat. No. 3,037,954 which discloses static vulcanization as well as the technique of dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured while continuously mixing and shearing the polymer blend. The resulting composition is a micro-gel dispersion of cured elastomer in an uncured matrix of thermoplastic polymer
In U.S. Pat. No. 4,141,863 a thermoplastic elastomer comprising a blend of rubber and a thermoplastic, high molecular weight polyester is described. The rubber component is a crosslinked homopolymer or copolymer of 1,3 butadiene. The use of the crosslinked rubber is said to improve the strength and toughness of the compositions.
Published European Patent Application No. 337,976 discloses thermoplastic elastomer compositions prepared from a blend of polyester resin and a covalently-crosslinked acrylate rubber. These thermoplastic elastomers are prepared by dynamic vulcanization and exhibit high temperature dimensional stability and low oil swell.
U.S. Pat. No. 5,093,426 teaches a combination of a thermoplastic resin such as a polyester with a specific copolymer rubber derived from alkyl acrylate, conjugated diene and another ethylenically unsaturated compound. The copolymer rubber is hydrogenated, then blended with the thermoplastic resin to provide a composition having superior low temperature performance, heat, ozone and oil resistance, mechanical strength and improved compression set.
In U.S. Pat. No. 5,216,074 a thermoplastic elastomer composition comprising a blend of thermoplastic resin with a hydrogenated diene polymer is described. The diene polymer is a high molecular weight block copolymer of segments of polybutadiene having low 1,2-vinyl content and segments of polybutadiene copolymer having high 1,2-vinyl content. This blend is said to have properties comparable to vulcanized rubber.